1. Field of the Invention
This invention relates to highly absorbent filaments and webs as well as methods for making them. More specifically, it pertains to filaments of chemically modified cellulose fibers and webs constructed from such filaments that exhibit, for aqueous systems, high absorbency and wicking properties which can be controlled and varied from slow to very fast making them particularly suitable for applications where it is desirable to draw a liquid away from a surface and concentrate it in a particular layer or location. Such applications include, by way of example and not limitation, disposable diapers, sanitary napkins, wipes, surgical sponges and the like.
2. Description of the Prior Art
The chemical modification of cellulose to increase its absorbency has been previously described and can be considered in a broad sense to fall into three major classifications in terms of methods:
(a) chemical substitution, etherization or esterification; PA1 (b) chemical substitution plus crosslinking; and PA1 (c) polymeric grafting.
For example, U.S. Pat. No. 3,670,069 to Mitchell is directed to absorbent fibers formed by extruding solutions such as those prepared from a hydroxyalkyl cellulose. As examples of category "(a)" above, Bernardin U.S. Pat. Nos. 3,658,790 and 3,691,154 disclose absorbent fibers and batt-like mats formed from phosphorylated cellulose or its acid form and products incorporating them. An example of category "(b)" above is U.S. Pat. No. 3,589,364 to Dean et al which discloses absorbent structures including cross-linked fibers of carboxymethyl cellulose and products made therefrom. Category "(c)" above is exemplified by the formation of acrylonitrile-grafted cellulose absorbent fibers and products as disclosed in U.S. Pat. Nos. 3,194,727 to Adams et al; 3,455,643 to Gruber et al; 3,065,041 to Suen; and 3,046,078 to Salsbury.